1. Field of the Invention
The present invention relates to a superconductor element including an oxide ceramic superconductor and a method of manufacturing the same.
2. Description of the Related Art
In recent years, a superconductor formed of an oxide ceramic material as a high-temperature superconductor has received a great deal of attention. Most of to such superconductors are oxide superconductors each having a perovskite structure containing a rare earth element. Such an oxide superconductor is confirmed to exhibit a superconducting property (i.e., a critical temperature is the liquid nitrogen temperature or more) at a high temperature of a liquid nitrogen temperature or more when its composition is properly selected. Along with the advance of fabrication techniques, an oxide superconductor having a higher critical temperature may be obtained. In addition, an oxide superconductor can be easily manufactured as compared with a conventional metal or intermetallic compound superconductor. Therefore, a superconductor element using such an oxide superconductor has been expected.
Most of the superconductor elements represented by a Josephson element include a superconductor/insulator/superconductor junction or superconductor/semiconductor/superconductor junction as its basic structure.
When an oxide superconductor as described above is applied to such a superconductor element, a coherence length of the superconductor is short and element characteristics greatly depend on a condition of the interface between the superconductor and the insulator or the like. In addition, it is difficult to form a good insulating film on an oxide superconductor. In other words, the oxide superconductor has poor junction property with any one of most materials. As an element using an oxide superconductor, samples have been prepared according to a point contact or slit type junction scheme in place of the superconductor/insulator/superconductor junction scheme.
An oxide superconductor also has poor junction property with a semiconductor such as Si or GaAs. Therefore, a sample element having a superconductor/semiconductor/superconductor junction is rarely manufactured.
In addition, an oxide superconductor has poor junction property with a metal. It is difficult to obtain an ohmic electrode having a sufficiently low contact resistance.
In order to achieve a superconductor element having good characteristics by using an oxide superconductor, therefore, an improvement of a poor property of a junction between a superconductor and an insulator, a semiconductor, or a metal is the major issue.